Complex behavior patterns are usually assumed to be associated with complex nervous organization. Yet little is known of the behavioral capacities of animals with primitive nervous systems. The aim of this study is to examine the integrative processes coordinating the behavior of Hydra. The structure of the nervous system in this animal is simple, that of a nerve net. Recent evidence suggests that much of its behavior is controlled by nonnervous mechanisms. Behavioral sequences are coordinated through interactions of groups of pacemakers rather than integrated by means of reflexes. Several questions are posed in this study. What degree of behavioral complexity is present in an animal coordinated primarily by non-nervous mechanisms? How are underlying pacemaker systems integrated to control behavior? How is such integration modified by sensory input into the systems? Is information stored in the patterning of electrical events? What are the physiological mechanisms underlying habituation in Hydra? Are such mechanisms different from other forms of behavioral inhibition? A range of electrophysiological techniques together with quantitative analyses of behavior will be employed as tools in this study. Methods of statistical analysis and computer simulation will be used to construct mathematical models describing integrative processes in this behavioral system. We hope to use such models to predict the behavior of the animal. What aspects of such models are common to other coelenterate systems? What techniques of analysis are appropriate for studying the patterning of electrical events in nonnervous systems? Have such techniques a wider application to the problem of pattern analysis of nervous impulses in higher animals?